The impersonalists do not have the power to go beyond the effulgence of God and arrive at the Personality of Godhead, from whom this effulgence is emanating. The Īśopaniṣad is a hymn to that Personality of Godhead. It is not that the impersonal Brahman is denied; it is also described, but that Brahman is revealed to be the glaring effulgence of the body of Lord Kṛṣṇa. And in the Caitanya-caritāmṛta we learn that Lord Caitanya is Kṛṣṇa Himself. In other words, Śrī Kṛṣṇa Caitanya is the basis of the impersonal Brahman.